The Alsport RTS series worked for me the best. I never got to ride a Dune Cycle . And I was never approached by them to be a dealer.
The small frame RTS worked good but had it's limits when people put in too big engines and did too much jumping I have seen frame breakage.
I have had all the small frame units and I did miss the hydraulic brakes that the big frame Street Legal units had but the calipers were Borg Warner and two lightweight for me. So I did replace them on my street machine. All history for me now but the dreams keep rolling along